Patients undergo video-EEG monitoring to determine seizure type and focus localization. Positron emission tomography (PET) and magnetic resonance imaging (MRI) are used to study the functional anatomy of language and memory activation, cerebral metabolism, blood flow, binding to neurotransmitter receptors, deposition of inflammatory markers, alterations in blood-brain barrier permeability and structure. Antiepileptic drug blood levels are obtained. Studies are performed in collaboration with NIMH and the NIH Clinical Center PET Department. The rate of atypical language was 2.5%) among healthy volunteers and 24.5% for patients. There was agreement between several classification methods, yet cluster analysis revealed novel correlations with clinical features. Beyond the established association of left-handedness, early seizure onset, and vascular pathology with atypical language, cluster analysis identified association of handedness with frontal lateralization, early seizure onset with temporal lateralization, and left hemisphere focus with a unilateral right pattern. Language dominance is a continuum; however, our results demonstrate meaningful thresholds in classifying laterality. Atypical language patterns are less frequent but more variable than typical language patterns, posing challenges for accurate presurgical planning. Language dominance should be assessed on a regional rather than hemispheric basis, and clinical characteristics should inform evaluation of atypical language dominance. Reorganization of language is not uniformly detrimental to language functioning. Based on our previous PET studies showing reduced 5HT1A receptor binding in TLE, have started a double-blind placebo-controlled cross-over trial of an experimental 5HT1A agonist in patients with epilepsy, to test the hypothesis that increased activation of this receptor may ameliorate both seizures and mood disorders. &#8232;&#8232; We used Freesurfer to segment cortical structures and obtain hippocampal volumes in 39 patients with intractable epilepsy. In addition, an investigator blinded to other data traced hippocampi manually on each slice. The main study outcome measure was the asymmetry index (AI) between hippocampal volume ipsilateral and contralateral to seizure foci compared between HHV-6 positive and negative patients. Viral DNA was isolated from fresh brain tissue obtained at temporal lobectomy. For 25 patients, viral detection was performed using quantitative real time PCR specific for HHV-6A and HHV-6B. For 14 patients, viral DNA detection was performed using digital droplet PCR (DdPCR) specific for HHV-6A and HHV-6B. HHV-6B was detected in 16 of 25 patients studied in the laboratory of Dr Steve Jacobson NINDS with quantitative real time PCR. For 14 studied with digital droplet PCR, one had HHV-6A, six HHV-6B, and three both viruses. On both Freesurfer and manual tracing, HHV-6-negative patients had significantly greater AI and lower ipsilateral volume than HHV-6 positive patients. Epilepsy duration and age of onset did not affect results. Our data suggest multiple potential etiologies for MTS. HHV-6 negative hippocampi had significantly greater preoperative atrophy than hippocampi positive for virus. HHV6 may have a less severe effect on hippocampus than other etiologies. In collaboration with Dr Robert Innis in NIMH, we studied patients with TLE and ligands binding to the TSPO receptor, highly expressed on activated microglia and reactive astrocytes. We found that ligand binding was higher in TLE patients than in controls for all temporal regions ipsilateral to seizure foci and in contralateral hippocampus, amygdala, and temporal pole. This study shows that TSPO binding is increased both ipsilateral and contralateral to seizure foci in TLE patients, suggesting ongoing inflammation. Anti-inflammatory therapy may have a role in treating drug-resistant epilepsy. We collaborated with Childrens National Medical Center in a trial of taurine for SSADH Deficiency. There is no established treatment for this disorder. One marketed antiepileptic drug, vigabatrin, although effective in the mouse model, is associated with substantial toxicity in man, and, moreover, has not been helpful for the patients who have tried it. NCS-382, a GHB receptor antagonist, had the highest survival rate of all interventions in the mutant animal model. However, there were significant alterations in blood chemistries found in NCS-382-treated mice. Taurine is abundant in various tissues, and has important roles in physiologic processes such as neuromodulation and osmoregulation. It may play a role in protection against free radical damage in neural tissus. Taurine increases chloride conductance in excitable tissues and binds to GABAA receptors (del Olmo et al 2000). The neuroprotective action of taurine against beta-amyloid and glutamate receptor agonists in chick retinal neurons is blocked by the GABAA antagonist picrotoxin (Louzada et al 2004). Taurine has demonstrable antiepileptic effects, and with increased seizure onset latency and reduced occurrence of tonic seizures in the parenteral kainic acid rodent epilepsy model. The mechanism was most consistent with an increase in GABA receptor function. Results did not show clinically meaningful improvement in the adaptive domains following taurine therapy. Transcranial magnetic stimulation was used to assess measures of cortical excitability found to be altered in our previous studies. We wished to test the hypothesis that patients with SSADH deficiency would have lengthening toward normal values of the cortical silent period, and return of short and long interval intracortical inhibition, during taurine treatment. We found preliminary evidence for increased cortical excitability parallels the lack of clinical effect; taurine may inhibit GABAA neurotransmission in SSADH deficiency and/or reduce the interval at which ICF occurs. Our data as well as other studies support the use of TMS as a biomarker for further clinical trials in SSADH deficiency. We initiated a trial of SGS-742, a GABAB receptor antagonist that has demonstrated good safety and tolerability in clinical trials of cognitive impairmen in patients age 8 years and older with SSADH deficiency. There is no proven therapy for this disorder. We will assess drug effects on cortical excitability as well as seizures, neuropsychological function, and other clinical parameters. We hope to establish validated markers in SSADH-deficient patients that can be measured during therapeutic intervention. The hypotheses to be tested are: 1: Patients will show improvement in the Auditory Comprehension subtest of the Neuropsychological Assessment Battery Language Module during treatment with SGS-742. 2: Patients with SSADH deficiency will have lengthening toward normal values of the cortical silent period, and return of long interval intracortical inhibition, during a therapeutic trial of SGS-742 3: Patients will show improvement on global assessment ratings Data from this study is relevant to conditions beyond SSADH deficiency, and will enhance our ability to understand inborn metabolic errors that present with phenotypes such as intellectual disability or autism spectrum disorder, and to make optimal therapeutic decisions in SSADH deficiency patients.